The present invention relates to a device for supplying a liquid to apparatuses which apply the liquid to substrates, thereby to process the substrates.
In the manufacture of a semiconductor device, a so-called "developing process" is performed. Generally, the developing process comprises the following steps. First, a substrate, e.g., a semiconductor wafer (hereinafter referred to as "wafer"), is mounted on a rotating table known as "spin chuck." (The wafer is coated with a resist film which has been exposed to light through a patterned mask.) Then, the spin chuck is rotated, thus spinning the wafer. A developing liquid is applied onto the spinning wafer from a liquid-applying member, such as a nozzle, located above the center of the wafer. The liquid spreads due to the centrifugal force acting on the wafer and is uniformly coated on the surface of the wafer. Thus, the resist film is developed.
The developing process is performed by a developer. The developing apparatus comprises a nozzle and a liquid supplying device. The liquid supplying device supplies a developing liquid to the nozzle. The liquid supplying device comprises a main tank, an intermediate tank, a flow rate adjuster, a filter, a temperature controller, and a valve. The main tank contains an amount of the developing liquid. The intermediate tank stores the developing liquid supplied from the main tank. The flow rate adjuster adjusts the rate at which the liquid is supplied to the nozzle. The filter removes impurities from the developing liquid. The temperature controller adjusts the temperature of the liquid at a desired value. The valve is provided to supply the developing liquid to the nozzle and stop supplying the same thereto.
The main tank, intermediate tank, flow rate adjuster, filter, temperature controller, and valve are connected in series in the order mentioned, by liquid passages (e.g., pipes). When the valve is opened, the developing liquid can be supplied to the nozzle. If a plurality of developers are installed, the same number of liquid supplying devices are used and operated independently, each connected to one developer. In each liquid supplying device, a specific gas is introduced into the intermediate tank, which is pressurized to a predetermined extent. The developing liquid is thereby supplied from the intermediate tank via the valve to the nozzle. Finally, the liquid is applied from the nozzle to the wafer.
When the surface of the developing liquid in the intermediate tank lowers to a lower-limit level, the supply of the gas into the intermediate tank is stopped. At the same time, the intermediate tank is depressurized through an evacuation pipe connected to the top of the tank and opening to the interior thereof. The developing liquid is thereby supplied into the intermediate tank from the main tank until the surface of the liquid in the intermediate tank rises to the upper-limit level. Even after the liquid is thus replenished, the depressurizing is continued for a predetermined time before the developer performs the developing process. The developing liquid in the intermediate tank is thereby degassed, expelling gases, such as O.sub.2 and N.sub.2, from the liquid.
A system comprising a plurality of developers, each having a liquid supplying device, is massive, and its manufacturing cost is high. The more developers the system has, the larger the system is, and the higher the manufacturing cost thereof is.
Further, the use efficiency of each light supplying device is low. This is because the apparatus supplies the liquid to the associated developer for a time much shorter than the time for which the developer performs the developing process on a wafer.
Still further, the efficiency of depressurizing the intermediate tank to degass the developing liquid contained therein is limited in the conventional. The depressurizing efficiency is proportional to the sectional area of the intermediate tank. Hence, the greater the diameter of the intermediate tank, the better. If the diameter of the tank is increased, however, the liquid supplying device will become proportionally large, and it will be difficult to supply the developing liquid stably and smoothly.